1. Field of the Invention
The present invention generally relates to a data processing device provided with a plurality of data processing units, wherein each data processing unit makes an access to a memory shared for data storage so as to perform an operation.
The present invention further relates to an image-forming device, which image-forming device can efficiently perform input/output operations of image signals of a digital copying machine, a facsimile, a printer, etc.
2. Description of the Related Art
Recently and continuing, the digitization of copying machines, etc., is in progress. Based on this progress, many image processing functions other than processing and editing images are becoming incorporated in the copying machines.
An example of such image processing functions is an electronic sorting function, which can dispense with the manual sorting operation by storing image data of a plurality of manuscripts in a memory and by providing a designated number of copies of manuscripts all at once. However, when the image data of the manuscripts is to be stored in the memory, the cost of the memory becomes high since the amount of image data is enormous. Accordingly, in order to reduce the memory cost, the following configurations are generally used.    1. First configuration—A semiconductor memory and a storage memory. A secondary storage device such as a hard disk device, which is less expensive than the semiconductor memory, is used as the storage memory (secondary memory).    2. Second configuration—A semiconductor memory is used as the storage memory. By reducing the data amount per image through image data compression operations, the necessary memory capacity is reduced.    3. Third configuration—A single memory is shared by a plurality of image input/output means (for example, an image scanner, a printer controller, a file server, and a facsimile controller).
For executing image input/output operations with respect to the memory, a memory controller (DMA controller) that uses a Direct Memory Access (DMA) data transfer method is often used. (See, for example, Japanese Laid-Open Patent Application No. 6-103225 and NO. 2000-158724.) The DMA controller performs access/data transfer with respect to a particular region of the memory based on memory region management information referred to as a descriptor, which management information indicates the procedure for the data transfer. It is also possible to perform the data transfer by dividing the memory region into which a single image is stored by a plurality of descriptors. For example, the memory may be used in the form of a ring buffer so as to execute input/output of the image data using less memory capacity as compared to the image data amount.
The memory access control using the DMA controller enables the system to keep track of current status of the data transfer (start and finish) designated by each descriptor and to control the execution timing of the data transfer (interruption or resumption of data transfer when accessing the image memory regions and interruption completion report of each descriptor, etc.). Accordingly, there are advantages such as high flexibility of timing control of access/data transfer with respect to the memories such as a semiconductor memory and a large-capacity secondary memory device, which are connected to the DMA controller, and a broad scope of application.
In the above-mentioned first configuration, generally, a plurality of data transfer operations (data writing operation and data reading operation) cannot be performed simultaneously with respect to a single memory device. Therefore, it is common to divide the data transfer (access) unit with respect to the secondary memory device by descriptors of the DMA controller. This is done in a time-multiplexed way so that it looks as if the plurality of data transfer operations are performed in parallel.
However, when such a time-multiplexed process is used, the overall amount of time needed for the data transfer is not reduced. Accordingly, in devices such as an image-forming device, in which the reduction in the amount of time needed for the input/output of image data has influence on the device productivity, the use of a time-multiplexed process may reduce the device productivity. Accordingly, in such an image-forming device, the above-mentioned second configuration may be employed, or a secondary memory device with a rapid data transfer rate may be implemented so as to reduce the time needed for the data transfer to the secondary memory device.
Further, in the image-forming device according to the related art, for the reason of simplifying the memory control, the time-multiplexed transfer is not preferably performed. Instead, in general, the secondary memory device is used as a resource and performs the data transfer approximately in phase with the image data input/output operation by the image input/output means.
In general, when compared with a first data transfer rate between the image input/output means and the semiconductor memory, a second data transfer rate between the semiconductor memory and the secondary memory device is low. The difference between the first data transfer rate and the second data transfer rate does not change even when the amount of data to be transferred to the secondary memory device is reduced by image compression. Therefore, the productivity of the image-forming device does not improve significantly even when the transferring timing of the data transfer process (including data conversion processes such as data compression, etc.) between the semiconductor memory and the secondary memory device is independently and appropriately controlled.
The transfer rate of the secondary memory device such as a hard disk device is improving year by year, and such improvement has also enabled an increasing productivity of the image-forming devices. However, a recent high-speed machine requires an even higher data transfer rate since such a machine reads both sides of the manuscript simultaneously; the processing ability (processing speed) of the image input/output means is improved; and further there are some machines with a mechanical constraint in that predetermined productivity cannot be realized unless the manuscript feeding process is performed in the non-interval mode. Accordingly, these days, the current data transfer (access) status with respect to the secondary memory device and the characteristics thereof, etc. are taken into consideration for switching between interval control and non-interval control of manuscript feeding.
Accordingly, with the recent improvements in devices such as an image-forming device as mentioned above, the data transfer rate with respect to the secondary memory device with large capacity such as a hard disk device, etc., is not always sufficient when compared with the data transfer rate with respect to the image input/output means even when the amount of data is reduced by data compression.
As an example, when image output means is to provide a color image from image data with multiple colors, the color image cannot be properly provided unless the image data stored in the secondary memory device is provided within a predetermined period of time, or the productivity of the device is significantly reduced since the time needed for providing the color image is long. Therefore, it is necessary for the image-forming device to cope with such a problem.
As another example, when a device such as an image-forming device is provided with a facsimile function, the facsimile transmission may be placed under restraint related to the data transfer time period in the protocol for data transfer using telephone lines. Accordingly, unless the data transmission is performed within a certain period of time, the connection is cut and thus the data cannot be transmitted. This facsimile transmission function is a typical function in such a device. Therefore, it is necessary for the image-forming device to cope with such a problem.
Further, when a device such as an image-forming device can perform a plurality of image signal input/outputs in parallel simultaneously, the efficiency of the image signal processing (input: storage, output: reading out) with respect to the secondary memory device becomes a key factor for improving the productivity of the image-forming device. However, under the current circumstances where there is a wide variety of image input/output means, it is becoming more challenging for the image-forming device to assure high productivity by maximally utilizing the memory device and capability of the data compression means.